[(−)-(6R,7R)]-7-((Z)-2-(2-Amino-4-thiazol)-2-hydroxyiminoacetamido)-8-oxo-3-vinyl-5-thia-1-azabicyclo[4.2.0]-oct-2-ene-2-carboxlic acid (IV), commonly known as cefdinir,

is a third generation semisynthetic cephalosporin for oral use, characterized by a broad antibacterial spectrum against gram-positive and gram-negative bacteria, its antibiotic activity being higher than that of other antibiotics for oral administration. In particular, it shows excellent antibacterial activity against staphylococci and streptococci.
Cefdinir is usually synthesized through intermediates of formula (V) wherein the hydroxyimino group (and optionally the primary amino group) is protected

R1 and R2 being as defined in the description.
According to the literature, the intermediates (V) can be obtained in different ways, but their recovery is troublesome and not convenient from the industrial standpoint.
For example, according to WO 97/24358, an intermediate of formula (V) wherein R1 is hydrogen and R2 is trityl (Va), is recovered as the salt with p-toluenesulfonic acid (VIa)

The drawback of this method is that the recovery is accomplished by adding to the reaction mixture anti-solvents such as ethers, which are dangerous and therefore not suitable for industrial use.
Other methods do not envisage recovery of the intermediates (V); as a consequence, the quality of the final product is poor and further purifications are required (WO 98/45299; Kamachi, H. et al., J. Antibiot. 1988 41(11), 1602-16).
Alternatively, the side chain can be linked to the cephalosporanic nucleus by means of subsequent synthetic steps, with decrease in the overall yield and increase in the process time (U.S. Pat. No. 4,559,334, EP 304019).
The intermediates (V) can also be recovered from water as free acids, but filtration and drying are very difficult.